Sensitizing silver halide emulsion



May i8, 1937. H. K. WEICHMANN 2,939,551

SENSITIZING SILVER HALIDE EMULSION Filed July 31, 1954 fg] I I I l j. c4 i I Patented May 18, 1937 UNITED STATES SENSITIZING SILVER HALIDEEMULSION Hans Konrad Weichmann, Dessau in Anhalt, Germany, assignor toAgfa Ansco Corporation, Binghamton, N. Y., a corporation of New YorkApplication July 31, 1934, Serial No. 737,853 In Germany August 3, 1933Claims.

My present invention relates to sensitizing silver halide emulsions.

One of its objects is a silver halide emulsion which has been renderedsensitive to waves for 5 which the emulsion is normally not sensitive.

Further objects will be seen from the detailed specication followinghereafter.

In the accompanying drawing there have been shown spectrograms of silverhalide emulsions according to this invention in comparison with a notspecially sensitized emulsion and an emulsion containing a knownsensitizer.

It has .already been proposed to sensitize a silver halide emulsion bythe incorporation of a benzoxo-indo-trimethinecyanine which is notsubstituted in the benzene nuclei. The emulsions thus sensitized are notsuited for the production of orthochromatic emulsions of a very highsensitivity inasmuch as the sensitizing power of these benzoXotrimethinecyanines is, for instance, not greater than that oferythrosine. Furthermore the range of sensitivity reaches only from theinitial sensitivity to about 590 au.

I have found that a. silver halide emulsion sensitized with abenzoxo-indo-trimethinecyanine which has been substituted preferably byan alkoxy group or an alkyl group or both in one or both benzene nucleiyields an orthochromatlc emulsion of highest sensitivity. Thesensitivity of the emulsions is greater than that obtained with the use'of the hitherto known sensitizers.

The sensitizing dyes may be obtained by condensing a quaternary ammoniumsalt of a benzoxazole or an indole with di-phenylformamidine in thepresence of acetic anhydride to form an intermediate product andcondensing the intermediate product with the desired indolenine orbenzoxazole respectively in the presence of pyridine, or the dyes may bemade by condensing an indolenine compound containing in a-position tothe nitrogen atom a methylene group capable of reaction of which onehydrogen atom has been substituted by the aldehyde group with aquaternary ammonium salt of a benzoxazole in solvents and in thepresence of a condensing agent, for instance, phosphoroxychloride orpiperidine.

By sensitizing a silver halide emulsion with a sensitizer according tothis invention the sensitiveness to green and yellow and simultaneouslythe total sensitivity is increased and in consequence a better renditionof the colors is obtained without aiecting the possibility to developthe exposed ernulsion in red light.

The spectrograms of the accompanying drawing show the high sensitivitywhich lies in a spectral region as it is desired, and it can easily berecognized that the unsubstituted benzoXo-indolenine-trimethinecyanineshave a much less in- G tense sensitizing effect.

such as pyridine, nitrobenzene, acetic anhydrine,

Figure 1 shows an unsensitized silver bromide emulsion, containing about4 per cent of silver iodide,

Figure 2 shows the same silver bromide emul- A sion sensitized with themost favorable amount of the unsubstitutedbenzoxo-indolenine-trimethinecyanine,

Figure 3 shows the same silver bromide emulsion sensitized with[B-ethyl-G-methoxy-benzoxazole (2) l [1.dimethyl- 3 -methyl indolenine(2) ltrimethinecyanine iodide,

Figure 4 shows the same silver bromide emulsion sensitized with[3ethylbenzoxazole(2) [1 .dimethyl.3 .5 .6 .trimethyl indolenine(2)ltrimethinecyanine perchlorate,

Figure 5 shows the same silver bromide emulsion sensitized with[3.5.6-trimethyl-benzoxazole (2) l-[l dimethyl- 3 .6 .dimethylindolenine (2) trimethinecyanine iodide,

Figure 6 shows the same silver bromide emulsion sensitized with[3ethy1-6.methoxyben zoxazole (2) l [1-dimethyl.dimethyl-indolenine (2)l-trimethinecyanine iodide,

Figure 7 shows the same silver bromide emulsion sensitized withi3.5.6-trimethyl-benzoxazole (2) i 1.dimethyl3 .5.6-trimethyl-indolenine(2) ltrimethinecyanine iodide.

The dyes are obtainable according to the desired solubility in form ofthe bromide, iodide, perchlorate etc. and are used in a quantity, suchas is usual for the known sensitizing dyes. This quantity may amount toabout l0 to 30 milligrams per kilo of emulsion ready for being castwhich contains about 9 per cent of gelatin, 4.5 per cent of silverhalide and the rest water. However, the invention is not limited to thequantities just indicated and the most suitable amount can be found ineach case by a few comparative experiments. The dyes may be added to theemulsion in form of solutions. Suitable solvents are the alcohols, forinstance, methyl or ethyl alcohol which may be used anhydrous or dilutedwith water. The dyes are applied to the emulsion during any stage of itsproduction; however, they are preferably added to the finished emulsionbefore casting.

The dyes may likewise be incorporated in the emulsion by coating thecast, but not dried, emulsion layer with a solution of the sensitizerin, for instance, aqueous or non-aqueous methyl alcohol or ethylalcohol, applied by means of a coating roller. The concentration of thesolution depends upon the speed of coating; for example, when the speedof coating amounts to 20 cm. per second, a suitable solution may consistof about 1 mgr. of

the sensitizer dissolved in cc. of aqueous methyl alcohol of 50 per centstrength. Another method of incorporating the sensitizer in the emulsionconsists in bathing the finished photographic material in a bath inwhich the dye is dissolved,

for instance, in a solution of methanol of per cent strength containing1 mgm-oi dye in 50 cc. of aqueous methanol.

The oxazole bases may be obtained'by distilling the suitably substitutedo-aminophenol with acetic anhydride. At :first water distills over andat a temperature above 200 C. the benzoxazole.

The following .examples illustrate the invention. Example 1L2rnethyl 6-methoxybenzoxazole is made by dlstilling the correspondinglysubstituted o-aminophenol with acetic anhydride. The compound distillsover at a temperature above 200 C.

2methylG-methoxybenzoxazole ethiodide is made by heating 15.6 grams ofethyliodide and 16.3 grams of 2-methyl-6-methoxy-benzoxazole for about 6to 8 hours on the steam bath. The compound separates in the form ofwhite needles. 5 grams of 2.methy1-S-methoxybenzoxazole with 3 grams ofdiphenylformamidine and 16 cc. of acetic anhydride are boiled for about5 min- After cooling the formed intermediate product is precipitatedwith ether and purined by washing with acetone. It is obtained in theform of a yellow powder.

The dye [3-ethyl-6-methoxybenzoxazole (2) l-[1dimethyl-3-rnethyl-indolenine (2)] trimethinecyanine iodidecorresponding with the formula is produced by heating a mixture oi 4grams oi.' the above intermediate product, 3 grams of 1.1.2.3-tetramethylindlenine and 15 cc. of pyridine for about 2 hours to 135 C.After cooling, the dye is precipitated by means oi.' a 10 per centaqueous solution of potassium iodide. 'Ihe dye is purified byrecrystallization i'rom alcohol and is obtained in the form of aredpowder.

The alcoholic solution of the dye has an absorption maximum at a wavelength oi' about 523 mi.

Incorporated in a silver bromide emulsion containing'about 4 per cent o!silver iodide the dye imparts to it a range of sensitivity from about500 to 610 mi with a maximum at about 570 nu.

Example -2.-2 methylbenzoxazole-p-toluenesulfoethylate is made bydistilling o-aminophenol and acetic anhydride, and heating the 2-methy1-benzoxazole obtained for about 8 hours to 140 C. with the equimolecularproportion of the ethylester of p-toluenesulfonic acid. 'Ihe compound iswashed with acetone and forms white crystals.

4 grams of 2-methylbenzoxazole-p-toluenesulfethylate and 3.5 grams oi'dlphenyltormamldine are boiled with 15 cc. of glacial acetic acid..AfterA cooling the intermediate product l"crystallizes in the form ofneedles on the addition of ether.

The dye [l-ethyl-benzoxazole (2)l-[1.dimeth yl.3.5.6trimethyl-indolenine (2)] trimethinecyanine perchlorate correspondingwith the formula CIB; C104 CH) tionmaximum at a wave taining about 4 percent ture assumes a red color and, after cooling the dye is precipitatedby the addition of 5 cc. ofva sorption maximum at a wave length oi.'about Incorporated in a silver bromide emulsion containing about 4 percent. of silver iodide, the dye imparts to. it a range of sensitivityfrom about 500 to 615 ,la with a maximum at about 570 up.

Example 3.12 grams of methyl-formaniline is mixed with 15 grams oiphosphorus oxychloride while stirring at room temperature. Stirring iscontinued for about 2 hours, then the mixture is diluted with 15 gramsof o-dichlorobenzene, cooled to 5 C., and mixed at this temperature with17 grams of 1.1.3.6-tetramethyl-2- methylindolenine. After about 15hours the mixture is distilled with steam and the non-volatile residueis, after drying, recrystallized from ligroin.

The aldehyde crystallizes in the i'orm oi' lightcolored crystals.

3 grams of 2.5.6-trimethylbenzoxazole dimethylsulfate which is producedanalogously to the other quaternary ammonium salts of benzoxazole and 2grams oi 1.1.3.5-tetramethylindolenine-2- methylene-w-aldehyde areboiled with 10 cc. of pyridine for about 1.5 hours. Then there are added5 cc. of a 10 per cent solution oi' potassium iodide. The red dye whichcorresponds with the formula Hao Hl (I) Hl C o-cn=on-cn=li zoxazole (2)l- 1-dimethy1-3.6dimethylindole nine 2) l trimethinecyanine iodidecorresponding with the formula H50 n.0 o Y H.

, J:-cH=oH-cn= N \N (1i/H5 \I y Ht is produced by boiling 3 grams of2-methyl-6- methoxybenzoxazole ethiodide (see Example 1) and 2 grams ofthe intermediate product described in Example 3 with 'I cc. of pyridinefor about 2 hours. After cooling the red dye is precipitated with asolution o! potassium iodide and recrystallized from alcohol. l

'I'he alcoholic solution of the dye has an absorplength of about 527 im.bromide emulsion conoi silver iodide, the dye imparts to it a range ofsensitivity from' about 500 to 615 m4 with a maximum at about 572 mi.

Example 5.-For producing 1.1.3.5.6penta methylindolenine-2-methylene-u-aldehyde, 12 grams of methylformaniline and 1 5grams oi' sulfurylchlorlde are mixed and stirred for about 2Incorporated in a silver hours. After diluting with 15 grams ofdichlorobenzene and cooling to 5 C. there are slowly added 18 grams of1.1.3.5.-pentamethyl-2-methyl indolenine while cooling. After about 15hours the mixture is distilled with steam and worked up as described inExample 3, whereby the aldehyde is obtained in the form of crystals.

The dye [3.5.6. trimethyl-benzoxazole (2) l-[1.dimethyl-3.5.ti-trimethyl-indolenine (2)] trimethinecyanine iodidecorresponding with the formula Incorporated in a silver bromide emulsioncontaining about 4 per cent of silver iodide, the dye imparts to it arange of sensitivity from about 500 to 618 'pu with a maximum at about575 im.

What I claim is: 1. A photographic material comprising a silverzoxo-indolenine-trimethinecyanine salt containing in one of the benzenenuclei a substituent of the group consisting of alkyl and alkoxy.

2. A photographic material comprising a' silverzoxo-indolenine-trimethinecyanine salt contain'- ing in both benzenenuclei a substituent of the group consisting of alkyl and'alkoxy.

3. A photographic material comprising a silver halide emulsioncontaining [3-ethyl-6-methoxybenzoxazole (2)l[1-dimethyl-3.6-dimethyl-indolenine (2) l-trimethinecyanine iodide.

4. A photographic material comprising a silver halide emulsioncontaining [3.5.6-trimethylbenzoxazole (2) l-1`dimethyl3.6.dimethyi-indolenine (2)] trimethinecyanine iodide.

5. A photographic material comprising a silver halide emulsioncontaining [3.5.6.trimethylbenzoxazole (2)l-l.l-dimethyl-3.5.6-trimethylindolenine (2)] trimethinecyanine iodide.

HANS KONRAD WEICHMANN.

